Quantitative Characterization of Grain Boundaries in Ultrafine-Grained Austenitic Stainless Steel by Cluster Analysis

A method is proposed for analyzing the relative energy distributions of grain boundaries in ultrafine-grained materials measured by grain boundary grooving using a scanning tunneling microscope. The grain boundary energy distribution in a grain boundary ensemble is considered as a superposition of individual distributions or populations, which can be identified by cluster analysis based on statistical criteria and each of which has its own average energy, variance, and share in the total distribution. The analysis is performed for 12Cr15Mn9NiCu steel with a coarse-grained structure in the as-received state and with an ultrafine-grained structure produced by hot helical rolling and subsequent cold rolling. It is shown that the number of boundary populations and their main characteristics revealed by clustering depend on the steel structure. The results of cluster analysis of experimental distributions are compared with the EBSD measurement data on grain boundary misorientation distributions. Discrepancy between the clustering results for the energy and misorientation distributions of grain boundaries is discussed taking into account the difference in the type of information obtained.